This project proposes to investigate the electrophysiologic alterations induced by myocardial ischemia in four models: 1) the isolated perfused mammalian heart; 2) human subjects sustaining acute myocardial infarction; 3) human subjects with occlusive coronary atherosclerosis during exercise; and 4) the superfused Purkinje fiber of the dog. Results to date have demonstrated that: 1) mean cardiac forces during activation and recovery in the isolated heart are often nondipolar, 2) surface summation methods for determing infarct size are sensitive not only to size but to lesion geometry and, 3) isopotential mapping is an insensitive method for assessing equivalent generator properties.